Led indicator light

ABSTRACT

To provide an LED lamp that is capable of achieving a desired luminous intensity distribution characteristic and producing uniform planar light emission, the LED lamp comprises a plurality of light emitting diodes and a cover lens so that light emitted by the plurality of light emitting diodes is output through the cover lens, wherein the cover lens has a plurality of prisms including a plurality of first prisms formed on the inner surface thereof, and direction and shape of the incident surfaces of the first prisms are set such that the first prisms output light in first luminous intensity distribution patterns that are substantially equal to each other.

TECHNICAL FIELD

[0001] The present invention relates to an LED lamp and, particularlyto, an LED lamp for traffic signal.

BACKGROUND ART

[0002] As light emitting diodes capable of emitting light of R, G and Bprimary colors and light emitting diodes capable of emitting white lightwith high luminance have been developed, LED lamps constituted from aplurality of light emitting diodes arranged in an array have been put inuse for various applications. The LED lamp has a far higher service lifethan that of an incandescent lamp, and also shows a high efficiency anda high resistance against vibration. For these advantages, the LED lamphas been used in advertising sign boards, traffic sign boards displayingroute guide or traffic information, light source for traffic signals andlarge screens.

[0003] With regards to the application of the LED lamp to trafficsignals, in particular, while the incandescent lamp used as the lightsource of the conventional traffic signal requires large reflectormirrors and color filters, the LED lamp has such advantages as thecapability to emit light of a single color that eliminates the need fora color filter and the capability to emit light with some degree ofdirectivity that eliminates the need to install a large reflectormirror.

[0004] Moreover, a traffic signal constituted from LEDs that does notneed reflector mirrors and color filters also has an advantage of beingfree from spurious lighting which is caused by extraneous light, thathas entered the traffic signal and reflected on the reflector mirrorplaced behind an incandescent lamp, coming out of the traffic signalthrough a color filter.

[0005] The LED lamp used in such a traffic signal or a sign board isusually installed at overhead height so as to be recognized by manypeople from a distance. As such, the LED lamp is required to emit lightwith symmetrical intensity distribution in the horizontal plane butasymmetrical intensity distribution in the vertical plane so that lightintensity is higher in the front field and the lower field.

[0006] As it has been made possible to increase the luminous intensityof light emitting diodes recently, it is enabled to decrease the numberof light emitting diodes required in an LED lamp. However, a new problemhas arisen that it is difficult to achieve planar light emission ofuniform intensity with an LED lamp consisting of a small number of lightemitting diodes that have high luminous intensity.

DISCLOSURE OF THE INVENTION

[0007] First object of the present invention is to provide an LED lampthat is capable of achieving a desired luminous intensity distributioncharacteristic.

[0008] Second object of the present invention is to provide an LED lampthat is capable of achieving a desired luminous intensity distributioncharacteristic and producing uniform planar light emission.

[0009] The LED lamp of the present invention, in order to achieve theobjects described above, comprises a plurality of light emitting diodesand a cover lens so that light emitted by the plurality of lightemitting diodes is output through the cover lens.

[0010] The cover lens has a plurality of prisms including a plurality offirst prisms formed on the inner surface thereof, and direction andshape of the incident surfaces of the first prisms are set such that thefirst prisms output light in first luminous intensity distributionpatterns that are substantially equal to each other.

[0011] The LED lamp of the present invention that has the constitutiondescribed above can emit light from the plurality of light emittingdiodes in a luminous intensity distribution pattern that corresponds tothe direction and shape of the incident surfaces of the first prisms.

[0012] The LED lamp of the present invention also allows the directionin which light that is output through the first prisms emerges in thevertical plane to be set by the direction of the incident surface, andthe direction in which light that is output through the first prismsdiffuses in the horizontal plane to be set by the configuration of theincident plane.

[0013] The LED lamp of the present invention preferably has such aconstitution as the plurality of prisms include also a plurality ofsecond prisms and the direction and shape of the incident surfaces ofthe second prisms are set so that the second prisms have second luminousintensity distribution patterns that are substantially equal to eachother.

[0014] Since the desired luminous intensity distribution pattern of theLED lamp can be achieved by means of the first and second prisms in theconstitution described above, better luminous intensity distributionpattern that is optimized can be achieved than in the case where theluminous intensity distribution pattern is formed with the first prismsonly.

[0015] This constitution allows the direction in which light that isoutput through the second prisms emerges in the vertical plane to be setby the direction of the incident surface, and the direction in whichlight that is output through the second prisms diffuses in thehorizontal plane to be set by the configuration of the incident surface.

[0016] In the LED lamp of the present invention, it is preferable thatthe first prisms and the second prisms form a pair and the pair ofprisms are arranged on the inner surface of the cover lens according toa certain rule, thereby achieving a uniform planar light emission on theexternal surface of the cover lens.

[0017] In the LED lamp of the present invention, the second prisms canbe formed so as to direct the light below the first prisms, which makesit possible to constitute the LED lamp that is required to emit lightwith higher intensity in the lower portion.

[0018] Further in the LED lamp of the present invention, the pluralityof light emitting diodes are preferably disposed in an arrangementpattern determined according to the luminous intensity distributionpattern required of the LED lamp. Since the desired luminous intensitydistribution characteristic of the LED lamp can be achieved by means ofthe arrangement pattern of the plurality of light emitting diodes, thefirst luminous intensity distribution pattern and the second luminousintensity distribution pattern in the constitution described above,better luminous intensity distribution pattern that is optimized toprovide the luminous intensity distribution characteristic describedabove can be achieved.

[0019] Also in the LED lamp of the present invention, the arrangementpattern is preferably set such that the number of light emitting diodeslocated below the horizontal plane that includes the central axis of thecover lens is set to 40% or less of the total number of the lightemitting diodes, in which case the LED lamp that is required to emitlight with higher intensity in the lower portion can be made easily.

[0020] Also in the LED lamp of the present invention, the angle betweenthe line, that connects the light emitting diode located at theoutermost position of the arrangement pattern and the periphery of thecover lens on the inner surface thereof, and the central axis of thecover lens is preferably in range from 30° to 60°. With thisconstitution, uniform planar light emission can be achieved on theexternal surface of the cover lens.

[0021] Moreover, in the LED lamp of the present invention, it ispreferable that the cover lens has the external surface that is aspherical surface of which radius of curvature is 500 mm or less.

[0022] With this constitution, when the first prisms or both the firstprisms and the second prisms are used, light emitted by the light sourcecan be output more efficiently. Also it is made possible to mitigate thereflection of extraneous light on the cover lens surface, therebypreventing the contrast from decreasing when lighted.

[0023] As described above, the present invention can provide the LEDlamp that is capable of achieving a desired luminous intensitydistribution characteristic and producing uniform planar light emission.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is an exploded perspective view of the LED lamp accordingto an embodiment of the present invention.

[0025]FIG. 2 is an enlarged perspective view of prisms formed on theinner surface of a cover lens according to an embodiment of the presentinvention.

[0026]FIG. 3 is a sectional view taken along lines A-A′ in FIG. 2.

[0027]FIG. 4 schematically shows the luminous intensity distributionpattern of light output through first prisms of this embodiment.

[0028]FIG. 5 schematically shows the luminous intensity distributionpattern of light output through second prisms of this embodiment.

[0029]FIG. 6 is a plan view of an LED assembly 1 of this embodiment.

[0030]FIG. 7 schematically shows the relative positions of the LEDassembly 1 and a cover lens 3 of this embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0031] Preferred embodiments of the present invention will be describedbelow with reference to the accompanying drawings.

[0032] As shown in FIG. 1, the LED lamp of this embodiment comprises acase 2 of truncated conical shape that has a circular base surface andan opening that is parallel to the base surface and has a diameterlarger than that of the base surface, an LED assembly 1 that has aplurality of light emitting diodes 11 disposed on a substrate 12 whichis attached to the base surface of the case 2, and a cover lens 3attached to the opening of the case 2, so that light is emitted in apredetermined luminous intensity distribution pattern for theapplication to traffic signal, having such construction as describedbelow.

[0033] For the purpose of forming the predetermined luminous intensitydistribution pattern with the LED lamp of this embodiment, the coverlens 3 has a plurality of prisms 30 comprising a pair of first prisms 31and second prisms 32 formed on the inner surface thereof.

[0034] Direction and shape of the incident surfaces of the first prisms31 are set so that the first prisms output light in intensitydistribution patterns that are substantially equal to each other.

[0035] Direction and shape of the incident surfaces of the second prisms32 are set so that the second prisms 32 output light in intensitydistribution patterns that are substantially equal to each other.

[0036] In the LED lamp of this embodiment, configuration of the secondprisms 32 is determined so as to direct light in a direction lower thanthat of the first prisms 31.

[0037] Specifically, the cover lens 3 of the LED lamp has one luminousintensity distribution pattern (first luminous intensity distributionpattern) formed by the assembly of the plurality of first prisms 31, andanother luminous intensity distribution pattern (second luminousintensity distribution pattern) formed by the assembly of the pluralityof second prisms 32 so as to form a luminous intensity distributionpattern as a whole through the superposition of the first and secondluminous intensity distribution patterns.

[0038] In the LED assembly 1 of the LED lamp, the plurality of lightemitting diodes 11 are arranged in an arrangement pattern that isdetermined according to the luminous intensity distribution patternrequired of the LED lamp.

[0039] Thus the luminous intensity distribution pattern of the LED lampin this embodiment is constituted by means of (1) the arrangementpattern of the plurality of light emitting diodes 11, (2) assembly ofthe plurality of first prisms 31 and (3) assembly of the plurality ofsecond prisms 32.

[0040] Now construction of components and the principle of forming theluminous intensity distribution pattern in the LED lamp according to theembodiment of the present invention will be described in more detailbelow.

[0041] (Prisms 30)

[0042] The prisms 30 comprise a pair of the first prisms 31 and thesecond prisms 32 that are disposed in a regular pattern on the innersurface of the cover lens 3 as shown in FIG. 2. In this embodiment, thefirst prisms 31 and the second prisms 32 are arranged alternately in thevertical direction and in the horizontal direction in a regular pattern.

[0043] In this specification, taking the situation where the LED lamp isusually used into consideration, the direction in the lateral planeparallel to the central axis of the cover lens 3 is referred to ashorizontal direction, and the direction perpendicular to the horizontalplane is referred to as vertical direction. According to thisdefinition, the direction of line A-A′ in FIG. 2 is the verticaldirection. Thus the prisms 30 comprise the pair of first prisms 31 andthe second prisms 32 that are disposed adjacent to each other in thevertical direction.

[0044] (First Prisms 31)

[0045] In this embodiment, each of the first prisms 31 has an incidentsurface consisting of a part of cylindrical surface.

[0046] The inclination of the incident plane of each of the first prisms31 is set such that light that is emitted by a light source located onthe central axis of the cover lens 3 (light source located at a positionwhere the LED assembly 1 is disposed) and is incident on the firstprisms 31 at the center C31 thereof emerges, after passing through thefirst prisms 31, in a direction parallel to the central axis of thecover lens 3 (schematically shown in FIG. 3 with reference numeral 101).

[0047] Radius and length of circumference of the cylindrical surfacethat constitutes the incident surface of the first prisms 31 are setsuch that light that is incident on the first prisms 31 and has passedtherethrough spreads to a predetermined extent in the horizontal plane,while longitudinal length of the cylindrical surface that constitutesthe incident surface in the direction perpendicular to thecircumferential surface of the cylinder that constitutes the incidentsurface is set such that light that is incident on the first prisms 31and has passed therethrough spreads to a predetermined extent in thevertical plane (plane perpendicular to the horizontal plane).

[0048] The cylindrical surfaces that constitute the incident surfaces ofthe first prisms 31 are formed to be substantially equal to each other.

[0049] The extents to which light incident on the incident surfaces ofthe first prisms 31 in the horizontal direction and in the verticaldirection are set in accordance to the luminous intensity distributionpattern required of the LED lamp in order to form the luminous intensitydistribution pattern required of the LED lamp.

[0050] The luminous intensity distribution patterns of the first prisms31 can be made equal to each other by forming the cylindrical surfacesthat constitute the incident surfaces of the first prisms 31substantially equal to each other and setting the inclination of theincident surface of each of the first prisms 31 such that light that isemitted by a light source located on the central axis of the cover lens3 is incident on the first prisms 31 at the center C31 thereof andemerges therefrom in a direction parallel to the central axis of thecover lens 3

[0051] In other words, direction and shape of the incident surfaces ofthe first prisms are set so that the luminous intensity distributionpatterns of light emerging from the first prisms 31 are equal to eachother in this embodiment.

[0052]FIG. 4 shows the light emerging through the first prisms 31 a, 31b of the two prisms 30 a, 30 b that are arbitrarily selected from amongthe plurality of prisms 30.

[0053] As shown in FIG. 4, in this embodiment, the luminous intensitydistribution patterns formed by the first prism 31 a and the luminousintensity distribution patterns formed by the first prism 31 b areformed so as to have the same extent in the horizontal direction and inthe vertical direction around the central axis of the cover lens 3located at the center thereof, while the luminous intensity distributionpatterns formed by the first prism 31 a and the luminous intensitydistribution patterns formed by the first prism 31 b are substantiallyequal to each other in terms of the direction and the pattern.

[0054] Although FIG. 4 shows as if the patterns agree only on animaginary screen S100 because the screen S100 that should be at asufficiently large distance is drawn near the cover lens 3 due to therestriction of drawing, actually diameter of the cover lens 3 issufficiently smaller than the proportion shown in the drawing and theluminous intensity distribution patterns substantially agree with eachother.

[0055] For example, it will easily be understood that the luminousintensity distribution patterns become identical when diameter of thecover lens 3 is made sufficiently smaller in FIG. 4.

[0056] As described above, light emitted from one light source makes oneluminous intensity distribution pattern (first luminous intensitydistribution pattern) through superposition of a plurality ofsubstantially identical luminous intensity distribution patterns thatare formed by different beams emerging from the plurality of firstprisms 31.

[0057] In this specification, the first luminous intensity distributionpattern formed by light that is output from one light source will bereferred to as first light intensity distribution pattern of singlelight source, in order to distinguish it from a luminous intensitydistribution pattern formed by light beams that are output from aplurality of light sources (light emitting diodes) to be describedlater.

[0058] (Second Prisms 32)

[0059] In this embodiment, each of the second prisms 32 has an incidentsurface consisting of a part of a cylindrical surface.

[0060] The inclination of the incident surface of each of the secondprisms 32 is set such that light that is emitted by a light sourcelocated on the central axis of the cover lens 3 and is incident on thesecond prisms 32 at the center C32 thereof emerges, after passingthrough the second prisms 32, in a direction parallel to each other andbelow the central axis of the cover lens 3 (schematically shown in FIG.3 with reference numeral 102).

[0061] Radius and length of circumference of the cylindrical surfacethat constitutes the incident surface of the second prisms 32 are setsuch that light that is incident on the second prisms 32 and has passedtherethrough spreads to a predetermined extent in the horizontal plane,while vertical length of the cylindrical surface that constitutes theincident surface is set such that light that is incident on the secondprisms 32 and has passed therethrough spreads to a predetermined extentin the vertical plane (plane perpendicular to the horizontal plane).

[0062] The cylindrical surfaces that constitute the incident surfaces ofthe second prisms 32 are formed to be substantially equal to each other.

[0063] The extents to which light incident on the incident surfaces ofthe second prisms 32 in the horizontal direction and in the verticaldirection are set in accordance to the luminous intensity distributionpattern required of the LED lamp in order to form the luminous intensitydistribution pattern required of the LED lamp.

[0064] The luminous intensity distribution patterns of light emergingfrom the second prisms 32 can be made equal to each other by forming thecylindrical surfaces that constitute the incident surfaces of the secondprisms 32 substantially equal to each other and setting the inclinationof the incident surface of the second prisms 32 such that light that isincident on the first prisms 31 at the central axis C31 thereof emerges,after passing through the first prisms 31, in directions parallel toeach other

[0065] In other words, direction and shape of the incident surfaces ofthe first prisms are set so that the luminous intensity distributionpatterns of the second prisms 32 are equal to each other.

[0066]FIG. 5 shows the light emerging through the second prisms 32 a, 32b of the two prisms 30 a, 30 b that are arbitrarily selected from amongthe plurality of prisms 30.

[0067] As shown in FIG. 5, in this embodiment, the luminous intensitydistribution patterns formed by the second prism 32 a and the luminousintensity distribution patterns of the second prism 32 b are formed soas to have the same extent in the horizontal direction and in thevertical direction, while the luminous intensity distribution patternsformed by the second prism 32 a and the luminous intensity distributionpatterns formed by the second prism 32 b are substantially equal to eachother in terms of the direction and the pattern.

[0068] Although FIG. 5 shows as if the patterns agree only on thespecific screen S100, this is due to the restriction of drawing.

[0069] It will be easily understood that, actually, the luminousintensity distribution patterns substantially agree with each other whendiameter of the cover lens 3 is made sufficiently smaller than theproportion shown in the drawing.

[0070] As described above, light emitted from one light source makes oneluminous intensity distribution pattern (second luminous intensitydistribution pattern), that is different from the first luminousintensity distribution pattern, through superposition of a plurality ofsubstantially identical luminous intensity distribution patterns thatare formed by different beams emerging from the plurality of secondprisms 32.

[0071] In this specification, the second luminous intensity distributionpattern formed by light that is output from one light source will bereferred to as second light intensity distribution pattern of singlelight source in order to distinguish it from a luminous intensitydistribution pattern formed by light beams that are output from aplurality of light sources (light emitting diodes) to be describedlater.

[0072] As will be understood from the above description, in thisembodiment, light emitted from one light source makes a luminousintensity distribution pattern (synthesized light intensity distributionpattern of single light source) through superposition of the first lightintensity distribution pattern of single light source and the secondlight intensity distribution pattern of single light source, by beingoutput through the cover lens 3.

[0073] (LED Assembly 1)

[0074] The LED assembly 1 is formed by disposing the plurality of lightemitting diodes 11 on the substrate 12 in a predetermined arrangement.In this embodiment, the arrangement pattern of the light emitting diodes11 and the intensity of light emitted by the LED are part of importantelements that determine the luminous intensity distribution pattern(characteristics) of the LED lamp along with the shape of the prism 30and arrangement of the prisms 30.

[0075] That is, in this embodiment, number of the light emitting diodes11 disposed in the upper row is made larger than the number of the lightemitting diodes 11 disposed in the lower row, so that the intensity oflight is different between the upper and the lower portions in the lightsource of the plurality of light emitting diodes, as shown in FIG. 6.Since this enables it to increase the intensity of light directed in thelower direction from the LED lamp, it is made possible to easily makethe LED lamp for traffic signal that is required to direct light ofhigher intensity in the lower direction by combining this with theconfiguration of the prisms 30 of the cover lens 30 describedpreviously. In our research, it has been confirmed that, when the LEDlamp for traffic signal is made by combining this with the configurationof the prisms 30 of the cover lens 30 described previously, it ispreferable to set the intensity of light emitted by the light emittingdiode 11 located below the optical axis of the LED assembly 1 to 40% orless of the intensity of light emitted by the light emitting diode 11located above the optical axis. Thus intensity of light may be madedifferent between the upper and lower portions either by the setting thenumber of light emitting diodes as described above, or by changing thecurrent drawn in the light emitting diodes or the luminance level of thelight emitting diodes.

[0076] (Luminous Intensity Distribution Pattern Formed by CollectiveLight Sources and Cover Lens 3)

[0077] The luminous intensity distribution pattern of the LED lamp as awhole will be described below in a case where the LED lamp isconstituted from a combination of the LED assembly 1 comprising thelight emitting diodes disposed in the arrangement pattern describedpreviously and the cover lens 3 of the constitution describedpreviously.

[0078] Now taking reference to FIG. 4, the luminous intensitydistribution patterns of the first prisms 31 a, 31 b shift downwardwhile maintaining the identical patterns when the light source isshifted to above the optical axis of the cover lens 3.

[0079] Also in FIG. 4, the luminous intensity distribution patternsformed by the first prisms 31 shift to the left of the optical axiswhile maintaining the identical patterns when the light source isshifted to the right of the optical axis of the cover lens 3.

[0080] Also in FIG. 4, the luminous intensity distribution patternsformed by the first prisms 31 shift to the right of the optical axiswhile maintaining the identical patterns when the light source isshifted to the left of the optical axis of the cover lens 3.

[0081] Even when the light source is located at a position offset fromthe optical axis of the cover lens 3, the first prisms 32 have identicalfirst light intensity distribution patterns of single light source whilethe first light intensity distribution pattern of single light sourcehas a direction that corresponds to the position of the light sourcerelative to the optical axis of the cover lens 3.

[0082] That is, when the LED assembly 1 comprising the plurality oflight emitting diodes 11 disposed in the predetermined arrangementpattern is used, the luminous intensity distribution pattern formed bythe LED assembly 1 and the first prisms 32 (first light intensitydistribution pattern of collective light source) is the superposition ofall the first light intensity distribution patterns of single lightsources formed by the individual light emitting diodes 11 and the firstprisms 32.

[0083] As will be clear from the above description, since the firstlight intensity distribution pattern of single light source formed bythe individual light emitting diode 11 has a direction that correspondsto the position of the light emitting diode 11, the first lightintensity distribution pattern of collective light source formed as thesuperposition of the first light intensity distribution patterns ofsingle light sources becomes a luminous intensity distribution patternthat corresponds to the arrangement pattern of the LED assembly 1.

[0084] When the number of the light emitting diodes 11 disposed abovethe optical axis of the cover lens 3 is made larger than the number ofthe light emitting diodes 11 disposed below the optical axis, forexample, the first light intensity distribution pattern of collectivelight source has a light intensity distribution that is stronger in thelower portion.

[0085] Now taking reference to FIG. 5, the luminous intensitydistribution patterns formed by the second prisms 32 a, 32 b shiftdownward while maintaining the identical patterns when the light sourceis shifted to above the optical axis of the cover lens 3.

[0086] Also in FIG. 5, the luminous intensity distribution patternsformed by the second prisms 32 shift to the left of the optical axiswhile maintaining the identical patterns when the light source isshifted to the right of the optical axis of the cover lens 3, while theluminous intensity distribution patterns formed by the second prisms 32shift to the right of the optical axis while maintaining the identicalpatterns when the light source is shifted to the left of the opticalaxis of the cover lens 3.

[0087] As described above, similarly to the case of the first prisms 31,even when the light source is located at a position offset from theoptical axis of the cover lens 3, the second prisms 32 have identicalsecond light intensity distribution patterns of single light sources,while the second light intensity distribution pattern of single lightsource has a direction that corresponds to the position of the lightsource relative to the optical axis of the cover lens 3.

[0088] That is, the second light intensity distribution pattern ofcollective light source formed by the LED assembly 1 and the firstprisms 32 is the superposition of all the second light intensitydistribution patterns of single light sources and becomes a luminousintensity distribution pattern that corresponds to the arrangementpattern of the LED assembly 1.

[0089] When the number of the light emitting diodes 11 disposed abovethe optical axis of the cover lens 3 is made larger than the number ofthe light emitting diodes 11 disposed below the optical axis, forexample, the second light intensity distribution pattern of collectivelight source has a light intensity distribution that is stronger in thelower portion.

[0090] To sum up, the luminous intensity distribution pattern of the LEDlamp formed by combining the LED assembly 1 and the cover lens 3 in thisembodiment is the luminous intensity distribution pattern formed bysynthesizing the first light intensity distribution pattern ofcollective light source formed by the arrangement pattern of the LEDassembly 1 and the first prisms 31 and the second light intensitydistribution pattern of collective light source formed by thearrangement pattern of the LED assembly 1 and the second prisms 32.

[0091] Thus the luminous intensity distribution pattern of the LED lampof this embodiment is achieved by combining (1) the arrangement patternof the plurality of light emitting diodes 11, (2) assembly of theplurality of first prisms 31 and (3) assembly of the plurality of secondprisms 32.

[0092] (Distance Between the Cover Lens 3 and the LED Assembly 1)

[0093] In the present invention, the distance between the cover lens 3and the LED assembly 1 is not restricted by the fact that the particularcover lens 3 and the LED assembly 1 are used.

[0094] However, the distance is preferably set within a range describedbelow in consideration of the directivity characteristic of the lightemitting diode and the required size of the LED lamp.

[0095] As shown in FIG. 7, it is preferable to set the distance betweenthe cover lens 3 and the LED assembly 1 such that the angle between theline, that connects the light emitting diode 11 located at the outermostposition of the LED assembly 1 and the periphery of the cover lens 3 onthe inner surface thereof, and the central axis of the cover lens 3 isnot larger than 60° C.

[0096] This is because this angle being larger than 60° C. leads toinsufficient intensity of light incident on a part located away from thecenter of the cover lens 3 due to the directivity characteristic of thelight emitting diode, thus making it impossible to achieve uniformplanar light emission (as the periphery of the cover lens darkens),resulting in lower efficiency of light emission.

[0097] It is also preferable to set the distance between the cover lens3 and the LED assembly 1 such that the angle between the line, thatconnects the light emitting diode 11 located at the outermost positionof the LED assembly 1 and the periphery of the cover lens 3 on the innersurface thereof, and the central axis of the cover lens 3 is 30° C. orlarger.

[0098] This is because this angle being smaller than 30° C. increasesthe light collecting power but leads to greater burden of diffusinglight imposed on the cover lens, thus resulting in lower efficiency oflight emission and larger profile of the LED lamp.

[0099] When the LED lamp is used outdoors in such an application astraffic signal, there may arise such a case as sunlight is reflected inthe outer surface of the cover lens resulting in decreasing contrastwhen illuminated. In order to mitigate the reflection of sunlight, theouter surface of the cover lens is preferably formed in a sphericalsurface having a radius of curvature not larger than 500 mm. Forming theouter surface with this curvature also allows it to suppress the heightof cut in the prisms and improve the efficiency of light emission.

[0100] Since the LED lamp of this embodiment described above isconstituted from a combination of the LED assembly 1 comprising theplurality of light emitting diodes disposed in the predeterminedarrangement pattern and the cover lens 3 having the plurality of prisms30, desired luminous intensity distribution pattern can be achieved witha simple construction.

[0101] Although the predetermined luminous intensity distributionpattern is formed by using the cover lens 3 having prisms 30 thatcomprise the pair of first prisms 31 and the second prisms 32 formed onthe inner surface thereof in a regular pattern and the LED assembly 1comprising the plurality of light emitting diodes disposed in thepredetermined arrangement in the preferred embodiment described above,the present invention is not limited to this constitution and may beimplemented with various modifications as follows.

[0102] Variation 1

[0103] While the predetermined luminous intensity distribution patternis formed by using the first prisms 31, the second prisms 32 and the LEDassembly 1 that comprises the plurality of light emitting diodesdisposed in the predetermined arrangement in the embodiment describedabove, the present invention may also be embodied by using only theplurality of first prisms 31 constituted similarly to the aboveembodiment, thereby forming the predetermined luminous intensitydistribution pattern.

[0104] For example, a relatively simple luminous intensity distributionpattern that is required to concentrate light with high intensity aroundthe optical axis of the cover lens can be achieved only by means of theplurality of first prisms 31 as shown in FIG. 4.

[0105] In this case, the arrangement of the light emitting diodes in theLED assembly may be a simple one such as concentric circles.

[0106] Variation 2

[0107] Similarly, the present invention may also be embodied by usingonly the plurality of second prisms 31 constituted similarly to theabove embodiment, thereby forming the predetermined luminous intensitydistribution pattern.

[0108] For example, a relatively simple luminous intensity distributionpattern that is required to concentrate light with high intensity in thelower portion can be achieved only by means of the plurality of secondprisms 31 as shown in FIG. 5.

[0109] In this case, the arrangement of the light emitting diodes in theLED assembly may be a simple one such as concentric circles.

[0110] Variation 3

[0111] Moreover, the present invention may also be embodied by usingonly the first prisms 31 and the second prisms 32 constituted similarlyto the above embodiment, thereby forming the predetermined luminousintensity distribution pattern.

[0112] In this case, the arrangement of the light emitting diodes in theLED assembly may be a simple one such as concentric circles.

INDUSTRIAL APPLICABILITY

[0113] According to the present invention, as described in detail above,it is made possible to provide an LED lamp that is capable of achievinga desired luminous intensity distribution characteristic and producinguniform planar light emission, and therefore traffic signals,information display apparatuses or the like that is capable of achievinga desired luminous intensity distribution characteristic and producinguniform planar light emission can be made by using this LED lamp.

1. A LED lamp comprising a plurality of light emitting diodes and acover lens so that a light emitted by the plurality of light emittingdiodes is output through the cover lens, wherein an inner surface ofsaid cover lens is provided with a plurality of prisms including aplurality of first prisms, directions and shapes of the first prisms areset so that said first prisms output light in first luminous intensitydistribution patterns that are substantially equal to each other.
 2. TheLED lamp according to claim 1; wherein a direction of the light that isoutput through said first prisms in the vertical plane is set by adirection of said incident surface, and a diffusion of the light that isoutput through said first prisms in the horizontal plane is set by theconfiguration of said incident plane.
 3. The LED lamp as in one ofclaims 1-2; wherein said plurality of prisms include a plurality ofsecond prisms and the directions and shapes of the incident surfaces ofsaid second prisms are set so that the second prisms have secondluminous intensity distribution patterns that are substantially equal toeach other.
 4. The LED lamp according to claim 3; wherein a direction ofthe light that is output through said second prisms in the verticalplane is set by a direction of said incident surface, and a diffusion ofthe light that is output through said second prisms in the horizontalplane is set by the configuration of said incident plane.
 5. The LEDlamp as in one of claims 3-4; wherein said first prisms and said secondprisms form pairs which are consist of one of said first prisms and oneof said second prisms, said pairs are arranged on the inner surface ofsaid cover lens according to a rule.
 6. The LED lamp as in one of claims3-5; wherein said second prisms are formed so as to direct the lightbelow the light output from said first prisms.
 7. The LED lamp as in oneof claims 3-6; wherein said plurality of light emitting diodes aredisposed in an arrangement pattern determined according to the luminousintensity distribution pattern required in the LED lamp.
 8. The LED lampaccording to claim 7; wherein said arrangement pattern is set so thatthe number of light emitting diodes located below the horizontal planethat includes the central axis of the cover lens is set to 40% or lessof the total number of the light emitting diodes.
 9. The LED lampaccording to claim 8; wherein the angle between the line, that connectsthe light emitting diode located at the outermost position of thearrangement pattern and the periphery of the cover lens on the innersurface thereof, and the central axis of the cover lens is in range from30° to 60°.
 10. The LED lamp as in one of claims 1-9; wherein said coverlens has the external surface that is a spherical surface of whichradius of curvature is 500 mm or less.